(discussion continues elseforum...)
For years I've written that size doesn't matter. And I've already posted my "five sizes" insight.
Now I'll try to tackle the issue from another direction.
Size does matter. But I know very few women, and only some men for whom size, as a partner, is a significant issue. There is a romance to larger sizes, but in practice, they're awkward.
Of the female, (and some male), partners I've know and who've expressed a preference, there are three issues dealing with physical size. The first issue is whether it can be inserted at all. And for some size combinations, that's an issue and it can be awkward. If he's particularly large and/or she's particularly small, then it can be difficult for them to fuck at all. And that's... of limited novelty value. If they can get it in, but he can't move without hurting her, that's of limited value. Frustrating, perhaps, and maybe exciting periodically, but probably not the sort of thing most people want to do several times a week. Or if each time they fuck, she tears and requires several weeks to heal, that's also something of a wet blanket on sex.
The second issue is whether the two of them can fuck in such a way that groins can bump and grind. There are numerous positions and movements that are particularly interesting and exciting that simply can't be accomplished if his length is much longer than hers.
Personally, I would hate this. Most of my good neurons are below my circumcision scar. If I could only fuck with the top half of my penis, I think it would probably not be worth the effort, frankly. It's one of the reasons I've only rarely enjoyed receiving oral. For me, being off size in that way would simply not be any fun. (Not for long, anyway. I do play with it with strap on's periodically.)
The third issue is cervix. If the two of you can fit together, and you can also fit together in such a way as to grind pelvises, then the next issue is whether there are positions that allow you to tickle her cervix. Few women enjoy having their cervix pounded right off, but many do enjoy cervix stimulation later in their arousal phase. The trick, then, is finding positions where this can happen, but doesn't necessarily have to.
If the two of you can fit all three of these criterion while fucking, in some position, (perhaps only female superior, perhaps only missionary), then you've got a pretty excellent match in terms of physical sizes, especially if the matching happens in positions that the two of you particularly enjoy.
Now the interesting thing is that very few people, men or women, are looking to date a penis or a vagina. Most of them are more interested in dating human beings who might sport them. Personality, physical distance between the two people's homes, children, smoking, politics, religion, and many others, can all be significant issues in selecting partners too and tend to be more important than physical compatibility for most people.
And we're really just talking about sizes for PIV fucking here. I know plenty of couples who have successful sexual relationships without PIV fucking. And for other activities, there are completely different size criterion. Hand sizes and finger lengths, for instance...
Chris.